Virus Resistance Induced in Plants by Polyacrylic Acid

SUMMARY Polyacrylic acid (PA) injected into tobacco cv. Xanthi-nc induced complete resistance to infection with TMV or tobacco necrosis virus but only partial resistance to potato virus X. The effect was maximal when the injection was made 2 to 3 days before inoculation. The lesion size was limited when the injection was made after inoculation. Using PA of 3500, 27000, 76000, 230000 and 1 × 106 mol. wt. the resistance decreased with increasing size of the polymer. In plants younger than 7 weeks, only the smallest polymer was active and evidence suggested that cell permeability to the larger polymers might increase with age of plant. The PA-induced resistance disappeared when plants were kept at 32 °C, but the effect of temperature was reversible. Polyacrylamide failed to induce resistance suggesting that the polyanionic structure of the acid polymers is responsible for the phenomenon. Disc-electrophoresis in 10% polyacrylamide gels showed that three additional soluble proteins appeared in PA-injected leaves, but only in conditions in which resistance to infection was induced. These new proteins co-electrophoresed with three out of four proteins produced in TMV-infected leaves of cv. Xanthi plants that also are resistant to infection and may be the cause of resistance.